1. Field of the Invention
This invention relates to an improved pump shell for a multistage metal working pump and particularly to a pump shell consisting of a plurality of pump shell units housed in a hollow cylindrical casing, each pump shell unit has an inner shell and an impeller, the inner shell has a novel positioning, and sealing structure to form a simple pump shell structure that may be made easily at low cost, and provide smooth fluid guiding with less turbulence and improved sealing.
2. Description of the Prior Art
Conventional multistage centrifugal pumps (such as submersible pumps, or also called as water-sunken pumps) mostly have a plurality of pump shell units and impellers stacked in series along a shaft. The shaft rotates the impellers against the pump shell and generates centrifugal force for fluid to flow in the passage through the pump shells. Traditionally, multistage pumps are made by casting. They are heavy, bulky, brittle, have low strength and lower pumping efficiency. Hence contemporary multistage pumps are increasing made by high strength and low weight metal working pumps.
The design consideration of a metal working pump usually includes cost of production and assembly, pumping efficiency, flow guide design, pressure resistance, sealing effect, and etc. Conventional metal working pumps seldom can totally make all of aforesaid factors to the optimum level.
For instance, EU Patent application No. 81110541 suggests a pump shell design shown in FIG. 1. It has a casing 11 made by a metal working process. Inside the casing 11, there are partition members 12 to form multistages 2 desired. Each stage 2 of the casing 11 includes an impeller 3 and baffles 20. The casing 11 of a stage 2 has a curved portion 19 formed in the circumference at a rear rim 111 for engaging with a front end of inner side 112 of an adjacent stage and to form an annular space therebetwen to squeeze a seal ring 14 therein. While it makes assembly of a multi stage pump easier, the fabrication of the curved portion 19 and front end 112 cannot always reach the precision required, and may result in not precise engagement between the two stages. Pumping thrust force and vibration may also cause deformation of the rim 111 and make the seal ring 14 become not effective for sealing function. Furthermore inside the casing 11, there is no smooth fluid guide in the fluid passage between the impeller 3 and baffles 20 and may induce turbulence at the front end of the impeller and result in poor pumping efficiency. Hence it has the disadvantages of poor axial alignment, poor sealing and lower pumping efficiency.
FIG. 2 shows another prior art of metal working pump disclosed in U.S. Pat. No. 5,234,317 which has a pump casing 21 made by pressing and stamping. The pump casing 21 has a U-shaped end rim 211 for engaging with another end of an adjacent stage pump casing. As the sealing area between the end rim 211 and another end is relatively small, the sealing effect is not good when subject to great pumping pressure or vibration. Furthermore, the casing 21 should be made by hydraulic or oil pressing, its cost is higher. And there is also no smooth fluid passage between the impeller and the baffles. It also is prone to produce turbulence and result in lower pumping efficiency.
FIG. 3 shows a further prior art of a metal working pump casing now available in the market place. It has a metal working shell 4 consisted of a front outer shell 41, a rear outer shell 42, a front inner shell 43, a rear inner shell 44, a diffuser 45, an impeller hub 46, a front seal ring 47 and an impeller (not shown in the figure). The front outer shell 41 has a front end plate 413, an indent axial holding side 411 and a radial holding side 412. The rear outer shell 42 has radial holding ends 421 and 422 for engaging respectively with the axial and radial sides 411 and 412 of an adjacent pump shell, and a holding end 441 for making contact with the front end plate 413 of the adjacent pump shell. The positioning and sealing effect is simpler and more effective. The curved inner portion of the front and rear inner shell 43 and 44 also may produce more streamline fluid flow and offers improved pumping efficiency. However it still has the following disadvantages:
1. Too many components. As shown in FIG. 3, the pump casing 4 has a total of eight components, including the front and rear outer shells 43, 44, diffuser 45, impeller hub 46, front seal ring 47 and impeller. It needs more molds and fabrication processes to produce. The cost becomes much higher. It also takes more assembly time and becomes more expensive.
2. It needs more precise machining. The engagement and sealing function between the holding ends 421, 422 and holding sides 411, 412 need more precise dimensions which cannot be made by conventional stamping or pressing operation. Extra machining work should be done. It increases production time and cost. The machining also makes the pump shell thinner and may reduce pump shell strength.
3. The front shells 41, 43 and rear shells 42, 44 should be joined by circular soldering at circular solder points 48. It costs much higher than spot soldering. Circular soldering also produces a not smooth or sightly appearance and inaccurate dimensions. It makes assembly more difficult. The soldering portion may temper material strength and needs extra machining work to reach dimension desired, and may result in a thinner pump shell and lower strength.
There are many other prior arts being disclosed, such as U.S. Pat. Nos. 4,877,372, 5,082,425, 5,344,678, 5,425,618, 5,201,848, 5,133,639, EU Pat. No. 0 492 575A1, 0 257 358A2, Pct No. WO 94/23211, DE Pat. No. 44 46 193C2. All of the above prior arts have some drawbacks and cannot fully satisfy the aforesaid design considerations such as production and assembly cost, enhanced flow passage and pumping efficiency, better pressure resistance and more effective sealing.
It is an object of this invention to provide an improved metal working pump shell for a multistage pump that has a fewer number of components, may be made and assembled at a lower cost, has strong pressure resistance and improved sealing.
It is another object of this invention to provide an improved metal working pump shell that may be used for a pump with a floatable impeller. The pump shell according to this invention includes a plurality of pump shell units stacked in series on a rotatable shaft. Each pump unit includes at least a hollow inner shell, an impeller, a sealing ring and a diffuser. The rotating shaft rotates the impeller in the shell for drawing fluid from an impeller inlet and discharging fluid to another pump unit at another stage.
The inner shell has an inner end which has one side fixedly engaged with the diffuser, an inner shell side formed with a curved connection with the inner end, and a step and taper holding end to form a curved connection with the inner shell side. Fluid flows into the impeller through an inlet at the holding end, passing around the curved connection of the inner shell side and through the outlet of the diffuser to be discharged into another impeller of the next adjacent pump unit. More than one pump unit is housed inside a hollow cylindrical casing.
The inner end may attach from its outside surface a holding ring which forms a sealing flange at one end to make a close engagement with the holding end of the next stage pump unit so that two pump units may be aligned and assembled easily and accurately. The holding end, and inner end and casing form a close compartment to hold and squeeze the seal ring therein for preventing leaking.
The impeller is floatable and has a rear wall mounted on an impeller hub and a front wall with an impeller front thrust ring attached thereon. The impeller hub has an impeller metal working member soldering with the rear wall of the impeller and an impeller plastic member mounting on the shaft and supporting the impeller metal working member. The impeller front thrust ring includes a thrust metal working member soldering to the front wall of the impeller around the impeller inlet and a thrust plastic member mounted on the thrust metal working member.
The holding ring also has a holding metal working member and a holding plastic member mating against the thrust plastic member of an adjacent pump unit to absorb axial thrust force during pumping operations.
The impeller hub is axially movable on the shaft and thus forms a floatable impeller that may move to a desired distance when subject to pumping thrust force.